1. Field of the Invention
The present invention relates to the accesses to SAN (Storage Area Network) disk storage, more specifically to an accessing system for disk storage that disperses the access load of each of those disk storage.
2. Description of Related Art
There is a well-known method in Japanese Unexamined Patent Publication (Kokai) JP 2000-099272 for sharing disk storage among a plurality of computers connected to those storage via a dedicated network such as fiber channel.
This technique is referred to as storage area network (SAN), which assures the high freedom in assignment of disk storage and computers so that a computer can be assigned to any of necessary disk storage areas flexibly.
In recent years, information handling systems that are accessed via the Internet are considered increasingly to be important. In particular, many computer systems have come to be built as Web servers for supplying various kinds of contents.
Such a Web server often includes an unspecific number of client computers, and accordingly it is accessed so frequently that it is difficult to estimate the peak time of accesses.
Japanese Unexamined Patent Publication (Kokai) JP 10-271447 and Japanese Unexamined Patent Publication (Kokai) JP 10-069467 disclose well-known methods for dispersing accesses to such a computer system so as to solve the above problem.
The JP 10-271447 reference discloses a technique for dividing for dispersing accesses in which each content is divided into small pieces so as to be stored in a plurality of disk storage.
In this case, the access load in proportion to the number of disk storage can be dispersed, but the technique cannot cope with accesses over an estimated value.
The JP 10-69467 also discloses a technique also for dispersing the access load with use of a plurality of server computers, but it is still difficult to disperse the load of each disk storage.
The SAN enables a plurality of computers to share a plurality of disk storage, but it cannot maintain its performance when the number of computers increases excessively, since the load of each of the shared disk storage increases.
Under the circumstances, it is an object of the present invention to provide a method for dispersing the access load of each disk storage, which can correspond to changes of the load of a disk storage on which accesses are concentrated from a plurality of the computers in the SAN.
In accordance with an aspect of the invention, a disk storage accessing system for enabling a plurality of computers to share an access a plurality of disk storage comprises a plurality of computers that refer to the disk storage, and a module for receiving an access path change command to change access paths for the computer to access a different disk storage according to the command. The system further comprises an instructing module for collecting and totaling a frequency of access to each disk storage, as counted by the counting module of each of the computers, as well as instructing a particular disk storage as a copy source disk storage to copy content in the copy source disk storage into one or more other disk storage as one or more target disk storage when the totaled access frequency is higher than a predetermined value, and for instructing the receiving module of a computer that accesses the copy source disk storage after receiving a report of copy completion, to change access paths so as to access a target disk storage instead of the copy source disk storage.
When instructing a computer that accesses a copy source disk to change access paths so as to access a target disk storage from the source disk storage, the instruction is directed to the computer that is the highest in the access frequency to the source disk storage.
When data in the copy source disk storage is updated, the updated data is copied into one or more of the target disk storage.